1. Field of Invention
The present invention relates to projection optical systems, production methods of the projection optical systems, and exposure apparatus including the projection optical system, in particular, projection optical systems which are suited for exposure apparatus to be used to manufacture microdevices such as semiconductor devices and liquid crystal display devices using a photolithography process.
2. Description of Related Art
It is known to use a method in which a pattern of a photomask (also called a reticle), after being reduction magnified, 4-5 fold, is formed onto a photosensitive substrate (an exposed substrate) such as a wafer to form an electronic device (microdevice) such as a semiconductor integrated circuit or a liquid crystal display. In this type of projection exposure apparatus, the exposure wavelength continues to shift towards a shorter wavelength in order to cope with the trend toward finer semiconductor integrated circuits.
Currently, a KrF excimer laser having an exposure wavelength of 248 nm is mainly used, but the ArF excimer laser with a shorter wavelength of 193 nm is beginning to be commercialized. In addition, a projection exposure apparatus using a light source which provides a beam in the wavelength band of the vacuum ultraviolet region such as an F2 laser with 157 nm wavelength, a Kr2 laser of 146 nm wavelength and an Ar2 laser of 126 nm wavelength is being considered. High resolution through a larger numerical aperture (NA) of a projection optical system is being achieved, and the development of a projection optical system having a larger numerical aperture, in addition to the development of a shorter wavelength for the exposure wavelength is ongoing.
Availability of optical material (lens material) having an excellent transmissiveness (transmittance) and uniform property for the exposure beam of a short wavelength in the vacuum ultraviolet region is limited. In a projection optical system with the ArF excimer laser as a light source, synthetic silica glass may be used as the lens material. However, with only one type of lens material, correction of chromatic aberrations cannot be achieved sufficiently. Hence, calcium fluoride crystal (fluorite) is used for some of the lenses. On the other hand, in a projection optical system using an F2 laser as a light source, in reality, calcium fluoride crystal (fluorite) is the only lens material that can be used.
Recently, the existence of intrinsic birefringence in a cubic (isometric) system calcium fluoride crystal (fluorite) for such vacuum ultraviolet rays with a short wavelength has been reported. In a super high precision optical system such as a projection optical system used in the manufacturing of electronic devices, the aberration generated in conjunction with birefringence of the lens material is fatal, and the use of a lens composition and lens design to substantially avoid the impact of birefringence is crucial.
Considering the aforementioned problems, aspects of the present invention aim to assure excellent optical performance substantially without receiving the impact of birefringence even if a crystal material with intrinsic birefringence, such as fluorite, is used.
In order to achieve the aforementioned objective, a first aspect of the invention relates to a production method of a projection optical system, of the type which projects an image of a first surface onto a second surface based on light having a predetermined wavelength and which includes at least one refractive member made of an isometric system crystal material that transmits the light having the predetermined wavelength. This aspect of the invention comprises a design step, including a sub-step of determining the direction of a crystal axis of the refractive member, made of at least one of the isometric system crystal material, while evaluating the light of a first polarization component and a second polarization component differing from the first polarization component, for obtaining the predetermined design data. This aspect of the invention also includes a crystal material preparation step of preparing the isometric system crystal material; a crystal axis measurement step of measuring the crystal axis of the isometric system crystal material; a refractive member formation step of forming a refractive member with a predetermined shape from the isometric system crystal material based on the design data in the design step; and an assembly step of arranging the refractive member based on the direction of the crystal axis of the refractive member obtained in the design step.
This aspect of the invention assures excellent optical performance because it enables the determination of the installation angle of the crystal axis of the refractive member made of the isometric system crystal material in such a manner that the impact of the birefringence is minimized while evaluating the impact of the birefringence caused by the isometric system crystal material in terms of a plurality of polarization components.
This aspect of the present invention also may include another step of preparing at least one refractive member with a predetermined birefringence distribution wherein the birefringence distribution is determined based on the design data in the design step. This aspect of the invention assures even more excellent optical performance because it enables the correction of the residual effect of birefringence which is reduced by optimization of the installation of the isometric system crystal material with the refractive member having the predetermined birefringence distribution.
The predetermined birefringence distribution may be at least one of a predetermined birefringence stress distribution of the refractive member and a birefringence distribution caused by a thin film provided on the refractive member.
The refractive member having the predetermined birefringence distribution may be made of silica or fluoride doped silica.
Preferably, the relationship, 0.6 less than xcfx86p/xcfx86cxe2x89xa61, is satisfied, where, xcfx86c is a clear aperture of the refractive member with the birefringence stress distribution, and xcfx86p is the light beam aperture of the light beam emitted from a predetermined point on the first surface when the light beam passes through the refractive member with the birefringence stress distribution. This aspect of the invention assures the position of the refractive member having the birefringence stress distribution to be the optimal position for correcting the birefringence caused by the isometric system crystal material using the refractive member having the birefringence stress distribution, namely, the position where the birefringence correction capability of the refractive member having the birefringence stress distribution is utilized as much as possible.
This aspect of the present invention may further comprise an aspherical surface creation step of forming the surface shape of at least one optical member in the projection optical system in an aspherical shape, wherein the aspherical shape is determined by the design data in the design step. This aspect of the invention enables the correction of a scalar component aberration (the aberration that does not depend on polarization direction) out of all the aberrations generated by the intrinsic birefringence of the isometric system crystal material using the aspherical surface.
The aspherical surface shape may include an asymmetric aspherical shape relative to the optical axis of the optical member.
The assembly step may comprise an optical performance measurement sub-step of measuring the optical performance of the assembled projection optical system, an optical member correction sub-step of changing the position and/or posture of at least one optical member in the projection optical system in order to make the measured optical performance be a predetermined optical performance, and an aspherical surface processing sub-step of forming the surface shape of at least one optical member in the projection optical system in order to make the measured optical performance be the predetermined optical performance. This aspect of the invention enables prevention of the deterioration of the optical performance caused by the integration error and the like of the optical member, because it enables the correction of low-order aberrations, for example, by adjusting position and posture of the optical member during manufacturing of the projection optical system, and enables the correction of high-order aberration of the aspherical surface to be set based on the measured optical performance.
The aspherical surface shape may be determined by considering the design data in the design step. This aspect of the invention enables the correction of both the aberration caused by the integration error of the optical member, and the scalar component aberration (the aberration that does not depend on polarization direction) among the aberrations caused by the intrinsic birefringence of the isometric system crystal material.
The assembly step may include an azimuth correction sub-step of correcting the azimuth around the optical axis of the refractive member made of the isometric system. This aspect of the invention enables the correction of the deterioration of the optical performance caused by the error in crystal axis direction in the refractive member made of the isometric system crystal material during the assembly of the projection optical system.
The assembly step may include a polarization optical performance measurement sub-step of measuring the optical performance of the assembled projection optical system regarding a plurality of polarization component light beams, and wherein an azimuth correction sub-step corrects the azimuth of the refractive member made of the isometric system crystal to make the optical performance regarding the plurality of polarization components assume a predetermined value based on the optical performance regarding the measured multiple polarization components. This aspect of the invention enables sufficient correction of a plurality of polarization component aberrations and scalar component aberrations because the projection optical system aberrations relating to a plurality of polarization components are measured during the assembly of the projection optical system, based on which measurements, the azimuth of the crystal axis of the refractive member made of the isometric system crystal material is adjusted.
The assembly step may include an optical performance measurement sub-step of measuring the optical performance of the assembled projection optical system and wherein the azimuth correction sub-step corrects the azimuth of the refractive member made of the isometric system crystal material to make the optical performance of the projection optical system assume the predetermined value based on the measured optical performance. This aspect of the invention enables sufficient correction of a projection optical system aberration because the projection optical system aberrations are measured during the assembly of the projection optical system, based on which measurements, the azimuth of the crystal axis of the refractive member made of the isometric system crystal material is adjusted.
The scalar aberration of the projection optical system may be measured, based on which measurement, the direction of the crystal axis of the refractive member made of the isometric system crystal material is preferably adjusted. At this time, a plurality of polarization component aberrations are estimated based on the measured scalar aberration, and the direction of the crystal axis of the refractive member made of isometric system crystal material is preferably further adjusted. This enables simplification of a production apparatus of a projection optical system.
The isometric system crystal material may be calcium fluoride or barium fluoride.
The predetermined wavelength may be less than or equal to 200 nm.
Another aspect of the invention includes a projection optical system produced by a production method as discussed above.
Another aspect of the present invention relates to a projection optical system in which an image of a first surface is projected onto a second surface based on a light beam having a predetermined wavelength, and includes: at least one isometric system refractive member made of an isometric system crystal material that transmits the light beam having the predetermined wavelength, and an amorphous refractive member made of an amorphous material for compensating deterioration of the optical performance due to the intrinsic birefringence of the isometric system refractive member. This aspect of the invention assures excellent optical performance because it enables the compensation for the deterioration of the optical performance caused by the intrinsic birefringence possessed by the isometric system refractive member made of the isometric system crystal material by using the amorphous refractive member.
The isometric system refractive member may be formed in such a manner that a crystal axis [100] or a crystal axis that is optically equivalent to the crystal axis [100] substantially coincides with the optical axis of the isometric system refractive member. This aspect of the invention enables the reduction of the effect of the intrinsic birefringence of the isometric system refractive member on the optical performance because the crystal axis [100] or the crystal axis that is optically equivalent to the crystal axis [100] substantially coincides with the optical axis of the isometric system refractive member, enabling the making of an angle that maximizes the impact of the birefringence of isometric system refractive member to be a relatively large angle relative to the optical axis.
The isometric system refractive member made of the isometric system crystal material may include a plurality of isometric system refractive members, and wherein the directions of the crystal axes of the plurality of isometric system refractive members are respectively determined in such a manner that the deterioration of the optical performance due to the intrinsic birefringence is reduced. This aspect of the invention assures excellent optical performance by reducing the compensation amount of birefringence in the amorphous refractive member, because it is possible to mutually offset the impact of the intrinsic birefringence of the plurality of isometric system refractive members by combining a plurality of the isometric system refractive members.
A maximum angle of the light beam passing through the isometric system refractive member, whose crystal axis direction is determined in such a manner that the deterioration of the optical performance due to the intrinsic birefringence is reduced, may be more than 20 degrees relative to the optical axis. This aspect of the invention reduces the impact of birefringence by applying the above correctional method to the isometric system refractive member, the maximum angle of which is larger than 20 degrees because the isometric system refractive member, the maximum angle of which relative to the passing light beam is more than 20 degrees and is easily effected by the intrinsic birefringence.
The isometric system refractive member whose crystal axis direction is determined in such a manner to reduce deterioration of the optical performance due to the intrinsic birefringence, may be arranged between a pupil position closest to the second surface side and the second surface of the projection optical system. This aspect of the invention reduces the impact of birefringence by applying the above correction method to the isometric system refractive member which is arranged between the pupil position closest to the second surface side and the second surface, because the isometric system refractive member arranged between the pupil position closest to the second surface side and the second surface is easily effected by the intrinsic birefringence.
The plurality of isometric system refractive members may comprise: a first group of radiation transmissive members which are formed in such a manner that a crystal axis [100] or a crystal axis that is optically equivalent to the crystal axis [100] substantially coincides with the optical axis, and a second group of radiation transmissive members which are formed in such a manner that the crystal axis [100] or the crystal axis that is optically equivalent to the crystal axis [100] substantially coincides with the optical axis, and wherein the first group of radiation transmissive members and the second group of radiation transmissive members have a positional relationship in which they are rotated substantially 45 degrees relative to each other around the optical axis.
The plurality of isometric system refractive members may comprise: a third group of radiation transmissive members which are formed in such a manner that a crystal axis [111] or a crystal axis that is optically equivalent to the crystal axis [111] substantially coincides with the optical axis, and a fourth group of radiation transmissive members which are formed in such a manner that the crystal axis [111] or the crystal axis that is optically equivalent to the crystal axis [111] substantially coincides with the optical axis, and wherein the third group of radiation transmissive members and the fourth group of radiation transmissive members have a positional relationship such that they are rotated substantially 60 degrees relative to each other around the optical axis.
The plurality of isometric system refractive members may comprise: a fifth group of radiation transmissive members which are formed in such a manner that a crystal axis [110] or a crystal axis that is optically equivalent to the crystal axis [110] substantially coincides with the optical axis, and a sixth group of radiation transmissive members which are formed in such a manner that the crystal axis [110] or the crystal axis that is optically equivalent to the crystal axis [110] substantially coincides with the optical axis, and wherein the fifth group of radiation transmissive members and the sixth group of radiation transmissive members have a positional relationship such that they are rotated substantially 90 degrees relative to each other around the optical axis.
The plurality of isometric system refractive members may comprise: a first group of radiation transmissive members which are formed in such a manner that the crystal axis [100] or the crystal axis that is optically equivalent to the crystal axis [100] substantially coincides with the optical axis, and a fifth group of radiation transmissive members which are formed in such a manner that the crystal axis [110] or the crystal axis that is optically equivalent to the crystal axis [110] substantially coincides with the optical axis.
In addition, the plurality of isometric system refractive members may further comprise: a third group of radiation transmissive members which are formed in such a manner that the crystal axis [111] or the crystal axis that is optically equivalent to the crystal axis [111] substantially coincides with the optical axis.
The plurality of isometric system refractive members, for which the crystal axis direction is determined in such a manner that the deterioration of the optical performance due to the intrinsic birefringence is reduced, may comprise a seventh group of radiation transmissive members formed in such a manner that the predetermined crystal axis substantially coincides the optical axis, and an eighth group of radiation transmissive members formed in such a manner that the predetermined crystal axis substantially coincides with the optical axis, and wherein an equation |L7xe2x88x92L8|/xcex less than 3xc3x9710+5 is satisfied, where L7 is an optical path length when the light beam corresponding to the maximum numerical aperture of the projection optical system passes through the seventh group of radiation transmissive members, L8 is an optical path length when the light beam corresponding to the maximum numerical aperture of the projection optical system passes through the eighth group of radiation transmissive members, and xcex is the predetermined wavelength. This aspect of the invention defines the optimal glass path length (optical path length) for the mutually offsetting ill effects of intrinsic birefringence using a plurality of isometric system refractive members.
The maximum value of the angle of the light beam passing through the seventh group and the eighth group of radiation transmissive members preferably is more than 20 degrees relative to the optical axis.
The seventh group and the eighth group of radiation transmissive members preferably are arranged between a pupil position closest to the second surface side and the second surface in the projection optical system.
This aspect of the present invention may further comprise an aspherical surface for reducing a scalar component of the deterioration of the optical performance due to the intrinsic birefringence. This aspect of the invention assures even more excellent optical performance because the scalar component aberration, in addition to the polarization component aberration caused by the intrinsic birefringence, is corrected.
The aspherical surface may have a rotationally asymmetric shape relative to the optical axis of the refractive member on which the aspherical surface is provided.
The amorphous refractive member may have a birefringence stress distribution. This aspect of the invention enables the correction of the effect of birefringence caused by the isometric system crystal material using the birefringence stress distribution, the birefringence amount of which is easily controlled.
The birefringence stress distribution may be generated due at least to impurities during the creation of the amorphous refractive member or the density distribution caused by a temperature program.
The amorphous optical member may be silica or fluoride doped silica.
The isometric refractive members preferably are made of calcium fluoride or barium fluoride.
Another aspect of the invention relates to a projection optical system which transfers an image of a first surface onto a second surface based on a light beam having a predetermined wavelength, comprising twin crystal refractive members made of a twin crystal that transmits the light beam having the predetermined wavelength. Twin crystals may be grouped into those in which two crystals with the same phase contact each other and have a directional relationship rotated 180 degrees around the crystal axis with a predetermined common low index, and those in which two crystals with the same phase contact each other and have a mirror image relationship relative to a predetermined crystal face. By using these twin crystals as the crystal refractive members in the projection optical system, deterioration of the optical performance caused by intrinsic birefringence may be reduced for the totality of the crystal refractive member because the effects of the birefringence are felt in the opposite direction at the twinning plane or at the front and the back of the twin boundary. By this construction, the optical performance of the projection optical system may be assured.
The twin boundary or twinning plane of the twin crystal refractive members may be determined in such a manner that the deterioration of the optical performance due to the intrinsic birefringence of the twin crystal is reduced even further. In this aspect of the invention, the position of the twin boundary or the twining plane is preferably the position where deterioration of optical performance due to the twin crystals"" intrinsic birefringence may be corrected.
The predetermined wavelength for this aspect of the invention may be less than or equal to 200 nm.
The above aspects of the invention can be applied to a projection exposure system in which an image of an original which is arranged on a first surface is projection exposed onto a workpiece arranged on a second surface by a light beam having a predetermined wavelength, comprising: a light source that supplies the light beam having the predetermined wavelength; an illumination optical system that guides the light beam from the light source to the original, and the projection optical system of any one of the aspects of the invention described above, arranged on an optical path between the first surface and second surface and which forms the image onto the second surface.
Another aspect of the invention relates to a projection exposure method in which an image of an original which is arranged on a first surface is projection exposed onto a workpiece arranged on a second surface by a light beam having a predetermined wavelength, comprising: supplying the light beam having the predetermined wavelength; illuminating the original using the light beam having the predetermined wavelength; and forming the image of the original onto the second surface using a projection optical system of any of the aspects of the invention described above, based on the illuminated light beams from the original.
The fact that the positional relationship of the first radiation transmissive member group and the second radiation transmissive member group is substantially rotated 45 degrees relative to each other around the optical axis means that the relative angle around the optical axis of a predetermined crystal axis (for example, [010], [001], [01-1] or [011]) which is directed to the different direction from the optical axis in the first radiation transmissive member and the second radiation transmissive member group is substantially 45 degrees. Here, if the crystal axis [100] is made to be the optical axis, because the rotational asymmetry of the effect of birefringence around the optical axis appears with a period of 90 degrees, having a rotational relationship of substantially 45 degrees relative rotation around the optical axis means the same as having a rotational relationship of substantially 45 degrees+(n * 90 degrees) relative rotation around the optical axis (n is an integer).
The fact that positional relationship of the third radiation transmissive member group and the fourth radiation transmissive member group is substantially rotated 60 degrees, relative to each other around the optical axis means that the relative angle around optical axis of a predetermined crystal axis (for example, [xe2x88x92111], [11-1], or [1-11]) which is directed to the different direction from the optical axis in the third radiation transmissive member and the fourth radiation transmissive member group is substantially 60 degrees. Here, if the crystal axis [111] is made to be the optical axis, because the rotational asymmetry of the effect of birefringence around the optical axis appears with a period of 120 degrees, having a rotational relationship of substantially 60 degrees relative rotation around the optical axis means the same as having a rotational relationship of substantially 60 degrees+(n * 120 degrees) relative rotation around the optical axis (n is an integer).
In aspects of the present invention, the fact that the positional relationship of the fifth radiation transmissive member group and the sixth radiation transmissive member group is substantially rotated 90 degrees relative to each other around the optical axis means that the relative angle around optical axis of a predetermined crystal axis (for example, [001], [xe2x88x92111], [xe2x88x92110] or [1-11]) which is directed to the different direction from the optical axis in the third radiation transmissive member and the fourth radiation transmissive member group is substantially 90 degrees. Here, if the crystal axis [110] is made to be the optical axis, because the rotational asymmetry of the impact of birefringence around the optical axis appears with a period of 180 degrees, having a rotational relationship of substantially 90 degrees relative rotation around the optical axis means the same as having a rotational relationship of substantially 90 degrees+(n * 180 degrees) relative rotation around the optical axis (n is an integer).
In order to achieve the above and/or other objectives, another aspect of the invention relates to a production method of a projection exposure apparatus which transfers an image of a first surface onto a second surface based on light having a predetermined wavelength and which includes at least one refractive member made of an isometric crystal material that transmits light having the predetermined wavelength. This aspect of the invention comprises a preparing step of preparing another refractive member which has at least one of a birefringence amount and a birefringence distribution that is different from that of the refractive member, and an exchanging step of exchanging the refractive member for the different refractive member.
In order to achieve the above and/or other objectives, another aspect of the invention relates to a production method of a projection exposure apparatus which transfers an image of a first surface onto a second surface based on light having a predetermined wavelength and which includes at least one refractive member made of an isometric crystal material that transmits light having the predetermined wavelength. This aspect of the invention comprises a preparing step of preparing a refractive member which has a predetermined birefringence distribution, and an adjusting step of adjusting at least one of a position and a posture of the refractive member which is arranged in the projection optical system, so as to adjust a polarization aberration of the projection optical system.
In order to achieve the above and/or other objectives, another aspect of the invention relates to a production method of an illumination optical system which is applied to a projection exposure apparatus which transfers an image of a first surface onto a second surface based on light having a predetermined wavelength. The illumination optical system includes at least one refractive member made of an isometric crystal material that transmits light having the predetermined wavelength. This aspect of the invention comprises a preparing step of preparing a refractive member made of the isometric crystal material, and an optimizing step of optimizing a crystal axis direction of the refractive member so as to correct a polarization aberration.